Understanding your eye prescription is not just a technical matter but a fundamental step to choose the right glasses, correctly evaluate lens materials, and check the quality of the optical service. Knowing the meaning of the abbreviations and values present in the prescription helps avoid mistakes and make informed purchases, even online.
The eye prescription can be issued in paper or electronic form. In both cases, it contains the main data of visual correction for each eye (right and left), indications for bifocal or progressive lenses, any values for the use of prism lenses, and, if indicated, the interpupillary distance (PD).
OD stands for "oculus dexter" (right eye), while OS means "oculus sinister" (left eye). These Latin abbreviations are universally used in eye prescriptions.
SPH (sphere) indicates the degree of myopia (-) or hyperopia (+). CYL (cylinder) is present if there is astigmatism and represents its intensity. AXIS completes the cylindrical value, indicating in degrees (from 0 to 180°) the orientation of the astigmatic correction.
ADD is the addition for near vision (presbyopia). PD is the interpupillary distance, essential for centering the lenses. PRISM and BASE are used in cases of ocular misalignment and require more complex evaluations.
Negative values (e.g., -2.50) indicate myopia: the eye sees well up close but poorly at a distance. Positive values (e.g., +1.75) indicate hyperopia: better vision at a distance but fatigue up close. Astigmatism is identified by the presence of CYL and AXIS, while ADD indicates the need for correction for presbyopia.
PD measures the distance (in mm) between the center of one pupil and the other. It is needed to perfectly center the lenses with the position of the eyes. It is particularly important in progressive glasses or with high corrections. It can be a single value (e.g., 62 mm) or divided by eye (e.g., 31/31 mm).
When requesting prescription sunglasses, the visual prescription remains the same, but additional variables must be considered: UV filter, lens coloring, possible polarization, and curvature of the frame. A dark lens with a wrap-around curve may require specific optical adjustments to maintain correct visual centering.
Single vision glasses have a single correction (for distance or near). Bifocal glasses feature an upper part for distance and a segment for near. Progressive glasses offer a smooth transition between distance, intermediate, and near. In the latter two cases, the prescription indicates ADD, which is the power addition necessary for near vision, usually ranging from +0.75 to +3.00.
Pediatric prescriptions require a more careful approach. Growing children may need checks every 6-12 months. Pediatric lenses often include shock-resistant, anti-reflective, and UV protection treatments. In some cases, prism lenses or weakly positive power may be prescribed even in the absence of severe visual defects to promote ocular development.
Once the data from the prescription is understood, it is possible to select the suitable lens. The material (polycarbonate, CR-39, glass, high transparency resins), the refractive index (e.g., 1.50, 1.60, 1.67, or 1.74), and the treatments (anti-reflective, blue light filter, photochromic) must be chosen based on the prescription values and daily needs.
In general, the eye prescription is valid for 1 year in children and adolescents, and for 1-2 years in adults, unless there are visual changes or particular conditions (diabetes, eye diseases, use of medications). If you experience visual fatigue, headaches, or worsening vision, it is advisable to schedule an earlier visit.
During the visit, it is useful to ask:
Generally, it is valid for 1 year for minors under 18 years and 1-2 years for adults. In case of eye diseases or rapid visual changes, the time may be reduced.
Yes, but the optical lab may slightly adjust the centering or curve of the lens based on the shape of the chosen sunglasses frame.
It means that the person is myopic: they have difficulty seeing at a distance and need a diverging lens with negative power.
Yes, it is essential to correctly center the lens in front of the pupil. If the data is missing, it can be measured directly in-store or with specific apps.
No. Contact lenses require a specific exam because they differ in distance between the lens and the eye. Values of SPH, CYL, and base curve are often different.
How to tell if you need prescription glasses: signals not to ignore
Correctly interpreting an eye prescription allows you to make more informed choices, select the right lenses, and verify the quality of the final product. Whether it’s prescription glasses, progressive lenses, or prescription sunglasses, knowing the technical terms puts you in the ideal position to communicate with opticians and professionals, avoiding mistakes and improving your visual experience.
